Method and apparatus for terminal self-reselecting resource based on priority in wireless communication system

ABSTRACT

Suggested is a novel condition for a media access control (MAC) entity in user equipment (UE) reselecting a sidelink resource in a wireless communication system. The MAC entity of the UE can reselect a sidelink resource when a configured sidelink grant does not satisfy a latency requirement according to ProSe per-packet priority (PPPP). More particularly, configuration is performed by an upper layer so that the MAC entity transmits on the basis of sensing using a resource pool; the MAC entity selects generation of a configured sidelink grant corresponding to transmission of a plurality of MAC protocol data units (PDU); and when data is available in a sidelink traffic channel (STCH) and the configured sidelink grant does not satisfy the latency requirement according to the PPPP, a sidelink resource is reselected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2017/010734, filed on Sep. 27, 2017,which claims the benefit of U.S. Provisional Applications No. 62/402,059filed on Sep. 30, 2016, and No. 62/402,074 filed on Sep. 30, 2016, thecontents of which are all hereby incorporated by reference herein intheir entirety

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications and, moreparticularly, to a method and apparatus for reselecting a resourceautonomously based on a priority in a wireless communication system.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

LTE-based vehicle-to-everything (V2X) is urgently desired from marketrequirement as widely deployed LTE-based network provides theopportunity for the vehicle industry to realize the concept of‘connected cars’. The market for vehicle-to-vehicle (V2V) communicationin particular is time sensitive because related activities such asresearch projects, field test, and regulatory work are already ongoingor expected to start in some countries or regions such as US, Europe,Japan, Korea, and China.

3GPP is actively conducting study and specification work on LTE-basedV2X in order to respond to this situation. In LTE-based V2X, PC5-basedV2V has been given highest priority. It is feasible to support V2Vservices based on LTE PC5 interface with necessary enhancements such asLTE sidelink resource allocation, physical layer structure, andsynchronization.

A user equipment is able to select a sidelink (SL) resource for V2Xcommunication by itself in a resource pool configured by a network.Thus, a method for selecting or reselecting an SL resource for V2Xcommunication needs to be discussed.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for reselecting aresource autonomously based on a priority in a wireless communicationsystem. The present invention provides a method and apparatus forenabling a user equipment to select and/or reselect a sidelink (SL)resource for vehicle-to-everything (V2X) communication autonomouslybased on a latency requirement dependent upon a ProSe per-packetpriority (PPPP).

In an aspect, a method for reselecting a sidelink resource by a mediaaccess control (MAC) entity of a user equipment (UE) in a wirelesscommunication system is provided. The method includes selecting toconfigure a sidelink grant corresponding to transmissions of multipleMAC protocol data units (PDUs), determining that there is data for avehicle-to-everything (V2X) communication in a sidelink traffic channel(STCH), determining that the configured sidelink grant cannot fulfil alatency requirement according to a ProSe per-packet priority (PPPP), andreselecting the sidelink resource. The MAC entity is configured by anupper layer to transmit based on sensing by using a resource pool.

The reselecting the sidelink resource may be performed for each sidelinkprocess configured for multiple transmissions based on sensing.

The reselecting the sidelink resource may include clearing theconfigured sidelink grant. The reselecting the sidelink resource mayinclude randomly selecting, with equal probability, an integer value inan interval between 5 and 15, and setting a value of a sidelink resourcereselection counter to the selected integer value. The reselecting thesidelink resource may include selecting a number of hybrid automaticrepeat request (HARQ) retransmissions from allowed numbers configured bythe upper layer in allowedRetxNumberPSSCH, and an amount of frequencyresources within the range configured by the upper layer betweenminRB-NumberPSSCH and maxRB-NumberPSSCH. The reselecting the sidelinkresource may include selecting an integer value in an interval between 1and 10 from allowed values configured by the upper layer inrestrictResourceReservationPeriod, and setting a resource reservationinterval by multiplying 100 with the selected integer value. Thereselecting the sidelink resource may include randomly selecting timeand frequency resources for transmission opportunities of sidelinkcontrol information (SCI) and sidelink shared channel (SL-SCH)corresponding to a number of transmissions of MAC PDUs with the resourcereservation interval from the resource pool, excluding resourcesindicated by a physical layer.

The upper layer may be a radio resource control (RRC) layer of the UE.

In another aspect, a user equipment (UE) in a wireless communicationsystem is provided. The UE includes a memory, a transceiver, and aprocessor, operably coupled to the memory and the transceiver, thatselects to configure a sidelink grant corresponding to transmissions ofmultiple media access control (MAC) protocol data units (PDUs),determines that there is data for a vehicle-to-everything (V2X)communication in a sidelink traffic channel (STCH), determines that theconfigured sidelink grant cannot fulfil a latency requirement accordingto a ProSe per-packet priority (PPPP), and reselects a sidelinkresource. A MAC entity of the UE is configured by an upper layer totransmit based on sensing by using a resource pool.

A UE is capable of efficiently selecting and/or reselecting an SLresource for V2X communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows 3GPP LTE system architecture.

FIG. 2 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 3 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 4 shows a method for reselecting an SL resource by an MAC entity ofa UE according to an embodiment of the present invention.

FIG. 5 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows 3GPP LTE system architecture. Referring to FIG. 1, the 3GPPlong-term evolution (LTE) system architecture includes one or more userequipment (UE; 10), an evolved-UMTS terrestrial radio access network(E-UTRAN) and an evolved packet core (EPC). The UE 10 refers to acommunication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10. An uplink (UL) denotes communication from the UE 10 to theeNB 20. A sidelink (SL) denotes communication between the UEs 10. In theDL, a transmitter may be a part of the eNB 20, and a receiver may be apart of the UE 10. In the UL, the transmitter may be a part of the UE10, and the receiver may be a part of the eNB 20. In the SL, thetransmitter and receiver may be a part of the UE 10.

The EPC includes a mobility management entity (MME) and a servinggateway (S-GW). The MME/S-GW 30 provides an end point of session andmobility management function for the UE 10. For convenience, MME/S-GW 30will be referred to herein simply as a “gateway,” but it is understoodthat this entity includes both the MME and S-GW. A packet data network(PDN) gateway (P-GW) may be connected to an external network.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The UEs 10 areconnected to each other via a PC5 interface. The eNBs 20 are connectedto each other via an X2 interface. Neighboring eNBs may have a meshednetwork structure that has the X2 interface. The eNB 20 is connected tothe gateway 30 via an S1 interface.

FIG. 2 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 3 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e., between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or Ipv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

A physical channel transfers signaling and data between PHY layer of theUE and eNB with a radio resource. A physical channel consists of aplurality of subframes in time domain and a plurality of subcarriers infrequency domain. One subframe, which is 1 ms, consists of a pluralityof symbols in the time domain. Specific symbol(s) of the subframe, suchas the first symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, and an uplink shared channel (UL-SCH)for transmitting user traffic or control signals. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both UL and DL. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

UL connections between logical channels and transport channels includethe DCCH that can be mapped to the UL-SCH, the DTCH that can be mappedto the UL-SCH and the CCCH that can be mapped to the UL-SCH. Downlinkconnections between logical channels and transport channels include theBCCH that can be mapped to the BCH or DL-SCH, the PCCH that can bemapped to the PCH, the DCCH that can be mapped to the DL-SCH, and theDTCH that can be mapped to the DL-SCH, the MCCH that can be mapped tothe MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Sidelink is described. Sidelink is a UE to UE interface for sidelinkcommunication and sidelink discovery. The Sidelink corresponds to thePC5 interface. Sidelink communication is AS functionality enablingproximity-based services (ProSe) direct communication, between two ormore nearby UEs, using E-UTRA technology but not traversing any networknode. Sidelink discovery is AS functionality enabling ProSe directdiscovery, using E-UTRA technology but not traversing any network node.

Sidelink physical channels include a physical sidelink broadcast channel(PSBCH) carrying system and synchronization related information,transmitted from the UE, a physical sidelink discovery channel (PSDCH)carrying sidelink discovery message from the UE, a physical sidelinkcontrol channel (PSCCH) carrying control from a UE for sidelinkcommunication, and a physical sidelink shared channel (PSSCH) carryingdata from a UE for sidelink communication. The sidelink physicalchannels are mapped to sidelink transport channels. The PSBCH is mappedto a sidelink broadcast channel (SL-BCH). The PSDCH is mapped to asidelink discovery channel (SL-DCH). The PSSCH is mapped to a sidelinkshared channel (SL-SCH).

In sidelink, the logical channels are also classified into controlchannels for transferring control plane information and traffic channelsfor transferring user plane information. The sidelink control channelsinclude a sidelink broadcast control channel (SBCCH) which is a sidelinkchannel for broadcasting sidelink system information from one UE toother UE(s). The SBCCH is mapped to the SL-BCH. The sidelink trafficchannels include a sidelink traffic channel (STCH) which is apoint-to-multipoint channel, for transfer of user information from oneUE to other UE(s). The STCH is mapped to the SL-SCH. This channel isused only by sidelink communication capable UEs.

Sidelink communication is a mode of communication whereby UEs cancommunicate with each other directly over the PC5 interface. Thiscommunication mode is supported when the UE is served by E-UTRAN andwhen the UE is outside of E-UTRA coverage. Only those UEs authorized tobe used for public safety operation can perform sidelink communication.

The UE supporting sidelink communication can operate in the followingtwo modes for resource allocation. The first mode is a scheduledresource allocation. The scheduled resource allocation may be calledMode 1. In mode 1, the UE needs to be RRC_CONNECTED in order to transmitdata. The UE requests transmission resources from the eNB. The eNBschedules transmission resources for transmission of sidelink controlinformation (SCI) and data. The UE sends a scheduling request (dedicatedscheduling request (D-SR) or random access) to the eNB followed by asidelink buffer status report (BSR). Based on the Sidelink BSR, the eNBcan determine that the UE has data for a sidelink communicationtransmission and estimate the resources needed for transmission. The eNBcan schedule transmission resources for sidelink communication usingconfigured sidelink radio network temporary identity (SL-RNTI).

The second mode is a UE autonomous resource allocation. The UEautonomous resource allocation may be called Mode 2. In mode 2, a UE onits own selects resources from resource pools and performs transportformat selection to transmit sidelink control information and data.There can be up to 8 transmission pools either pre-configured for out ofcoverage operation or provided by RRC signalling for in-coverageoperation. Each pool can have one or more Prose per-packet priority(PPPP) associated with it. For transmission of a MAC protocol data unit(PDU), the UE selects a transmission pool in which one of the associatedPPPP is equal to the PPPP of a logical channel with highest PPPP amongthe logical channel identified in the MAC PDU. There is a one to oneassociation between sidelink control pool and sidelink data pool. Oncethe resource pool is selected, the selection is valid for the entiresidelink control period. After the sidelink control period is finished,the UE may perform resource pool selection again.

A UE is considered in-coverage for sidelink communication whenever itdetects a cell on a public safety ProSe carrier. If the UE is out ofcoverage for sidelink communication, it can only use Mode 2. If the UEis in coverage for sidelink communication, it may use Mode 1 or Mode 2as per eNB configuration. If the UE is in coverage for sidelinkcommunication, it shall use only the resource allocation mode indicatedby eNB configuration unless one of the exceptional cases occurs. When anexceptional case occurs, the UE is allowed to use Mode 2 temporarilyeven though it was configured to use Mode 1. Resource pool to be usedduring exceptional case may be provided by eNB.

The cell on the public safety ProSe carrier may select one of thefollowing two options. First, the cell on the public safety ProSecarrier may provide a transmission resource pool for Mode 2 in SIB18.UEs that are authorized for sidelink communication may use theseresources for sidelink communication in RRC_IDLE in the cell on the samecarrier (i.e. public safety ProSe carrier). UEs that are authorized forsidelink communication may use these resources for sidelinkcommunication in RRC_IDLE or RRC_CONNECTED in a cell on another carrier.

Alternatively, the cell on the public safety ProSe carrier may indicatein SIB18 that it supports sidelink communication but does not providetransmission resources. UEs need to enter RRC_CONNECTED to performsidelink communication transmission. In this case the cell on the publicsafety ProSe carrier may provide in broadcast signalling an exceptionaltransmission resource pool for Mode 2, to be used by the UE inexceptional cases. A UE in RRC_CONNECTED that is authorized to performsidelink communication transmission indicates to the serving eNB that itwants to perform sidelink communication transmissions. The eNB validateswhether the UE is authorized for sidelink communication transmissionusing the UE context received from MME. The eNB may configure a UE bydedicated signalling with a transmission resource pool for Mode 2 thatmay be used without constraints while the UE is in RRC_CONNECTED.Alternatively, the eNB may configure a UE to use the exceptionaltransmission resource pool for Mode 2 which the UE is allowed to useonly in exceptional cases, and rely on Mode 1 otherwise.

A set of transmission and reception resource pools for sidelink controlinformation when the UE is out of coverage for sidelink communication ispre-configured in the UE. The resource pools for sidelink controlinformation when the UE is in coverage for sidelink communication areconfigured as below. The resource pools used for reception areconfigured by the eNB via RRC, in broadcast signaling. The resource poolused for transmission is configured by the eNB via RRC, in dedicated orbroadcast signaling, if Mode 2 is used. The resource pool used fortransmission is configured by the eNB via RRC, in dedicated signaling ifMode 1 is used. The eNB schedules the specific resource(s) for sidelinkcontrol information transmission within the configured reception pools.

A set of transmission and reception resource pools for data when the UEis out of coverage for sidelink communication is pre-configured in theUE. The resource pools for data when the UE is in coverage for sidelinkcommunication are configured as below. The resource pools used fortransmission and reception are configured by the eNB via RRC, indedicated or broadcast signaling, if Mode 2 is used. There is noresource pool for transmission and reception if Mode 1 is used.

Sidelink discovery is defined as the procedure used by the UE supportingsidelink discovery to discover other UE(s) in its proximity, usingE-UTRA direct radio signals via PC5. Sidelink discovery is supportedboth when UE is served by EUTRAN and when UE is out of EUTRA coverage.Only ProSe-enabled public safety UE can perform sidelink discovery whenit is out of EUTRA coverage. For public safety sidelink discovery, theallowed frequency is pre-configured in the UE, and is used even when UEis out of coverage of E-UTRA in that frequency. The pre-configuredfrequency is the same frequency as the public safety ProSe carrier.

There are two types of resource allocation for discovery messageannouncement. The first type is a UE autonomous resource selection,which is a resource allocation procedure where resources for announcingof discovery message are allocated on a non UE specific basis. The UEautonomous resource selection may be called Type 1. In Type 1, the eNBprovides the UE(s) with the resource pool configuration used forannouncing of discovery message. The configuration may be signaled inbroadcast or dedicated signaling. The UE autonomously selects radioresource(s) from the indicated resource pool and announces discoverymessage. The UE can announce discovery message on a randomly selecteddiscovery resource during each discovery period.

The second is a scheduled resource allocation, which is a resourceallocation procedure where resources for announcing of discovery messageare allocated on per UE specific basis. The scheduled resourceallocation may be called Type 2. In Type 2, the UE in RRC_CONNECTED mayrequest resource(s) for announcing of discovery message from the eNB viaRRC. The eNB assigns resource(s) via RRC. The resources are allocatedwithin the resource pool that is configured in UEs for announcement.

For UEs in RRC_IDLE, the eNB may select one of the following options.The eNB may provide resource pools for Type 1 based discovery messageannouncement in SIB19. UEs that are authorized for sidelink discoveryuse these resources for announcing discovery message in RRC_IDLE. Or,the eNB may indicate in SIB19 that it supports sidelink discovery butdoes not provide resources for discovery message announcement. UEs needto enter RRC_CONNECTED in order to request resources for discoverymessage announcement.

For UEs in RRC_CONNECTED, a UE authorized to perform sidelink discoveryannouncement indicates to the eNB that it wants to perform sidelinkdiscovery announcement. A UE can also indicate to the eNB thefrequency(s) in which sidelink discovery announcement is desired. TheeNB validates whether the UE is authorized for sidelink discoveryannouncement using the UE context received from MME. The eNB mayconfigure the UE with resource pool for Type 1 for discovery messageannouncement via dedicated signaling. The eNB may configure resourcepool along with dedicated resource in the form of time and frequencyindices for discovery message announcement via dedicated RRC signaling.The resources allocated by the eNB via dedicated signaling are validuntil the eNB re-configures the resource(s) by RRC signaling or, the UEenters RRC_IDLE.

Authorized receiving UEs in RRC_IDLE and RRC_CONNECTED monitor resourcepools used for Type 1 and resource pools for Type 2. The eNB providesthe resource pool configuration used for discovery message monitoring onintra frequency, inter frequency of same or different PLMNs cells in RRCsignaling (SIB19). The RRC signaling (SIB19 or dedicated) may containdetailed sidelink discovery configuration used for announcement ofsidelink discovery in cells of intra-frequency, inter-frequency of sameor different PLMNs.

Vehicle-to-everything (V2X) communication is described. V2Xcommunication contains the three different types, i.e.vehicle-to-vehicle (V2V) communications, vehicle-to-infrastructure (V2I)communications, and vehicle-to-pedestrian (V2P) communications. Thesethree types of V2X can use “co-operative awareness” to provide moreintelligent services for end-users. This means that transport entities,such as vehicles, road side unit (RSU), and pedestrians, can collectknowledge of their local environment (e.g. information received fromother vehicles or sensor equipment in proximity) to process and sharethat knowledge in order to provide more intelligent services, such ascooperative collision warning or autonomous driving.

V2X service is a type of communication service that involves atransmitting or receiving UE using V2V application via 3GPP transport.Based on the other party involved in the communication, it can befurther divided into V2V service, V2I service, V2P service, andvehicle-to-network (V2N) service. V2V service is a type of V2X service,where both parties of the communication are UEs using V2V application.V2I service is a type of V2X service, where one party is a UE and theother party is an RSU both using V2I application. The RSU is an entitysupporting V2I service that can transmit to, and receive from a UE usingV2I application. RSU is implemented in an eNB or a stationary UE. V2Pservice is a type of V2X service, where both parties of thecommunication are UEs using V2P application. V2N service is a type ofV2X service, where one party is a UE and the other party is a servingentity, both using V2N applications and communicating with each othervia LTE network entities.

In V2V, E-UTRAN allows such UEs that are in proximity of each other toexchange V2V-related information using E-UTRA(N) when permission,authorization and proximity criteria are fulfilled. The proximitycriteria can be configured by the mobile network operator (MNO).However, UEs supporting V2V service can exchange such information whenserved by or not served by E-UTRAN which supports V2X service. The UEsupporting V2V applications transmits application layer information(e.g. about its location, dynamics, and attributes as part of the V2Vservice). The V2V payload must be flexible in order to accommodatedifferent information contents, and the information can be transmittedperiodically according to a configuration provided by the MNO. V2V ispredominantly broadcast-based.

V2V includes the exchange of V2V-related application information betweendistinct UEs directly and/or, due to the limited direct communicationrange of V2V, the exchange of V2V-related application informationbetween distinct UEs via infrastructure supporting V2X Service, e.g.,RSU, application server, etc.

In V2I, the UE supporting V2I applications sends application layerinformation to RSU. RSU sends application layer information to a groupof UEs or a UE supporting V2I applications.

In V2P, E-UTRAN allows such UEs that are in proximity of each other toexchange V2P-related information using E-UTRAN when permission,authorization and proximity criteria are fulfilled. The proximitycriteria can be configured by the MNO. However, UEs supporting V2Pservice can exchange such information even when not served by E-UTRANwhich supports V2X service. The UE supporting V2P applications transmitsapplication layer information. Such information can be broadcast by avehicle with UE supporting V2X Service (e.g. warning to pedestrian),and/or by a pedestrian with UE supporting V2X Service (e.g. warning tovehicle). V2P includes the exchange of V2P-related applicationinformation between distinct UEs (one for vehicle and the other forpedestrian) directly and/or, due to the limited direct communicationrange of V2P, the exchange of V2P-related application informationbetween distinct UEs via infrastructure supporting V2X service, e.g.,RSU, application server, etc.

In V2X communication, messages such as common awareness messages (CAM),decentralized environmental notification messages (DENM), or basicsafety messages (BSM) may be transmitted. The CAM includes informationon a vehicle's type, a location, speed, a direction, etc., and may beperiodically broadcasted by any vehicle. The DENM includes informationon a type of a particular event and an area where the particular eventhas occurred, and may be broadcasted by an RSU or a vehicle. The BSM isincluded in the U.S. J2735 basic safety message, and have similarcharacteristics to those of the CAM. Through the BSM, an emergency brakewarning, a front collision warning, an intersection safety support, ablind spot and line departure warning, a overtake warning, anout-of-control warning service may be provided.

The UE may autonomously select the SL resource for V2X communicationwithin the resource pool configured by the network. That is, the UE mayselect autonomously the SL resource for V2X communication in Mode 2 andperform V2X communication via the corresponding SL resource. However, SLresources for V2X communication may be selected based on sensing. Morespecifically, the UE may perform sensing for (re)-selection of SLresources. Based on the sensing result, the UE may (re)-select aspecific SL resource and may reserve a plurality of SL resources. UEautonomous resource selection based on sensing for V2X communication maybe referred to as SL mode 4.

SL grant reception and SCI transmission according to the conventionalart are described in detail. In order to transmit on the SL-SCH, the MACentity must have at least one sidelink grant. Sidelink grants areselected as follows for sidelink communication.

1> if the MAC entity is configured to receive a single sidelink grantdynamically on the PDCCH and more data is available in STCH than can betransmitted in the current SC period, the MAC entity shall:

2> using the received sidelink grant determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

2> consider the received sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was received, overwriting apreviously configured sidelink grant occurring in the same SC period, ifavailable;

2> clear the configured sidelink grant at the end of the correspondingSC Period;

1> else, if the MAC entity is configured by upper layers to receivemultiple sidelink grants dynamically on the PDCCH and more data isavailable in STCH than can be transmitted in the current SC period, theMAC entity shall for each received sidelink grant:

2> using the received sidelink grant determine the set of subframes inwhich transmission of SCI and transmission of first transport blockoccur;

2> consider the received sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was received, overwriting apreviously configured sidelink grant received in the same subframenumber but in a different radio frame as this configured sidelink grantoccurring in the same SC period, if available;

2> clear the configured sidelink grant at the end of the correspondingSC Period;

1> else, if the MAC entity is configured by upper layers to transmitusing one or multiple pool(s) of resources and more data is available inSTCH than can be transmitted in the current SC period, the MAC entityshall for each sidelink grant to be selected:

2> if configured by upper layers to use a single pool of resources:

3> select that pool of resources for use;

2> else, if configured by upper layers to use multiple pools ofresources:

3> select a pool of resources for use from the pools of resourcesconfigured by upper layers whose associated priority list includes thepriority of the highest priority of the sidelink logical channel in theMAC PDU to be transmitted;

2> randomly select the time and frequency resources for SL-SCH and SCIof a sidelink grant from the selected resource pool. The random functionshall be such that each of the allowed selections can be chosen withequal probability;

2> consider the selected sidelink grant to be a configured sidelinkgrant occurring in those subframes starting at the beginning of thefirst available SC Period which starts at least 4 subframes after thesubframe in which the sidelink grant was selected;

2> clear the configured sidelink grant at the end of the correspondingSC Period;

Sidelink grants are selected as follows for V2X sidelink communication.

1> if the MAC entity is configured to receive a sidelink grantdynamically on the PDCCH and data is available in STCH, the MAC entityshall:

2> using the received sidelink grant determine the number of HARQretransmissions and the set of subframes in which transmission of SCIand transmission of a transport block occur;

2> consider the received sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitbased on sensing using a pool of resources, the MAC entity selects tocreate a configured sidelink grant corresponding to transmissions ofmultiple MAC PDUs, and data is available in STCH, the MAC entity shallfor each Sidelink process configured for multiple transmissions based onsensing:

2> if SL_RESOURCE_RESELECTION_COUNTER=0 and the MAC entity randomlyselects, with equal probability, a value in the interval [0, 1] which isabove the probability configured by upper layers in probResourceKeep; or

2> if the configured sidelink grant cannot accommodate a RLC servicedata unit (SDU) by using the maximum allowed MCS configured by upperlayers in maxMCS-PSSCH and the MAC entity selects not to segment the RLCSDU; or

2> if a pool of resources is configured or reconfigured by upper layers:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] and set SL_RESOURCE_RESELECTION_COUNTER to the selectedvalue;

3> select the number of HARQ retransmissions from the allowed numbersconfigured by upper layers in allowedRetxNumberPSSCH, and an amount offrequency resources within the range configured by upper layers betweenminRB-NumberPSSCH and maxRB-NumberPSSCH;

3> select an integer value in the interval [1, 10] from the allowedvalues configured by upper layers in restrictResourceReservationPeriodand set the resource reservation interval by multiplying 100 with theselected value;

3> randomly select the time and frequency resources for transmissionopportunities of SCI and SL-SCH corresponding to the number oftransmissions of MAC PDUs with the resource reservation interval fromthe resource pool, excluding the resources indicated by the physicallayer. The random function shall be such that each of the allowedselections can be chosen with equal probability;

3> if the number of HARQ retransmissions is equal to 1 and there areavailable resources, except the resources already excluded by thephysical layer:

4> randomly select the time and frequency resources for the othertransmission opportunities of SCI and SL-SCH corresponding to the numberof additional transmissions of the MAC PDUs with the resourcereservation interval from the available resources. The random functionshall be such that each of the allowed selections can be chosen withequal probability;

4> consider a set of transmission opportunities which comes first intime as the selected sidelink grant and a set of transmissionopportunities which comes later in time as the retransmissionopportunities;

3> else:

4> consider the set as the selected sidelink grant;

3> use the selected sidelink grant to determine the set of subframes inwhich transmissions of SCI and SL-SCH;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

2> else if SL_RESOURCE_RESELECTION_COUNTER=0 and the MAC entity randomlyselects, with equal probability, a value in the interval [0, 1] which isless than or equal to the probability configured by upper layers inprobResourceKeep:

3> clear the configured sidelink grant, if available;

3> randomly select, with equal probability, an integer value in theinterval [5, 15] and set SL_RESOURCE_RESELECTION_COUNTER to the selectedvalue;

3> use the previously selected sidelink grant for the number oftransmissions of the MAC PDUs with the resource reservation interval todetermine the set of subframes in which transmissions of SCI and SL-SCHoccur;

3> consider the selected sidelink grant to be a configured sidelinkgrant;

1> else, if the MAC entity is configured by upper layers to transmitbased on either sensing or random selection using a pool of resources,the MAC entity selects to create a configured sidelink grantcorresponding to transmission(s) of a single MAC

PDU, and data is available in STCH, the MAC entity shall for a Sidelinkprocess:

2> select the number of HARQ retransmissions from the allowed numbersconfigured by upper layers in allowedRetxNumber PSSCH, and an amount offrequency resources within the range configured by upper layers betweenminRB-Number PSSCH and maxRB-NumberPSSCH;

2> if transmission based on random selection is configured by upperlayers:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

2> else:

3> randomly select the time and frequency resources for one transmissionopportunity of SCI and SL-SCH from the resource pool, excluding theresources indicated by the physical layer. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;

2> if the number of HARQ retransmissions is equal to 1:

3> if transmission based on random selection is configured by upperlayers and there are available resources for more transmissionopportunity:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> else, if transmission based on sensing is configured by upper layersand there are available resources, except the resources already excludedby the physical layer, for more transmission opportunity:

4> randomly select the time and frequency resources for the othertransmission opportunity of SCI and SL-SCH corresponding to additionaltransmission of the MAC PDU from the available resources. The randomfunction shall be such that each of the allowed selections can be chosenwith equal probability;

3> consider a transmission opportunity which comes first in time as theselected sidelink grant and a transmission opportunity which comes laterin time as the retransmission opportunity;

2> else:

3> consider the transmission opportunity as the selected sidelink grant;

2> use the selected sidelink grant to determine the subframes in whichtransmission(s) of SCI and SL-SCH occur;

2> consider the selected sidelink grant to be a configured sidelinkgrant;

The MAC entity shall for each subframe:

1> if the MAC entity has a configured sidelink grant occurring in thissubframe:

> if the configured sidelink grant corresponds to transmission of SCI:

3> instruct the physical layer to transmit SCI corresponding to theconfigured sidelink grant;

3> for V2X sidelink communication, deliver the configured sidelink grantand the associated HARQ information to the Sidelink HARQ Entity for thissubframe;

2> else if the configured sidelink grant corresponds to transmission offirst transport block for sidelink communication:

3> deliver the configured sidelink grant and the associated HARQinformation to the Sidelink HARQ Entity for this subframe.

There is ongoing discussion concerning selection or reselection of an SLresource.

Hereinafter, various aspects of an SL resource for V2X communicationaccording to various embodiments of the present invention will bedescribed.

1. Procedure for (re)selecting one resource for each SL process

According to the above-described conventional method for SL grantreception and

SCI transmission, resource reselection is used to allocate multipletransmission opportunities of SCI and SL-SCH. If resource reselection istriggered, a UE allocates multiple transmission opportunities as below.

1) Step 1: The UE selects a value of SL_RESOURCE_RESELECTION_COUNTERbetween [5, 15].

2) Step 2: The UE selects an integer value between [1, 10] and sets aresource reservation period by multiplying the selected value by 100. Inthis step, the UE is likely to set a resource reservation periodaccording to an actual message transmission period from among 100 ms,200 ms . . . 1000 ms.

3) Step 3: The UE randomly select a time resource and a frequencyresource for multiple transmission opportunities, together with aresource reservation period, from a resource pool. In this step,whenever SL_RESOURCE_RESELECTION_COUNTER is 0, a SL may be reselected.Thus, if the resource reservation period is 100 ms, the SL resource isideally allocated up to SL_RESOURCE_RESELECTION_COUNTER at an intervalof 100 ms.

This resource allocation mechanism is intended to support an actual V2Xtraffic pattern (for example, a V2X message periodically generated at aninterval of 100 ms). This mechanism is substantially similar tosemi-persistent scheduling (SPS) allocation. SPS may operate for eachlogical channel or each PPPP. Thus, even associating one resource(re)selecting procedure with one logical channel or one PPPP ispossible.

As described above, it may be considered that one resource (re)selectingprocedure is associated with transmission of a plurality of MAC PDUs forone SL process. According to an embodiment of the present invention, itmay be suggested to associate one resource (re)selecting procedure withone logical channel or one PPPP for transmission of the plurality of MACPDUs. To this end, the following options may be considered.

1) Option 1: One (re)selecting procedure may be associated with onelogical channel or one PPPP. In this option, an MAC entity may selectgenerating a configured SL grant corresponding to transmission of aplurality of MAC PDUs for an STCH (or an STCH associated with one PPPP).The MAC entity may inspect whether data is available in the STCH. TheMAC entity may perform multiple transmission procedures for each STCH(or each PPPP). According to Option 1, the conventional SL reception andlegacy SCI transmission may be changed as shown in Table 1.

TABLE 1   ...   1> else, if the MAC entity is configured by upper layersto transmit based on sensing using a pool of resources, the MAC entityselects to create a configured sidelink grant corresponding totransmissions of multiple MAC PDUs for a STCH (or for STCH(s) associatedwith one PPPP), and data is available in the STCH, the MAC entity shallfor each STCH (or PPPP) configured for multiple transmissions based onsensing:   ....

2) Option 2: One logical channel or one PPPP may be associated with oneSL process. In this option, the MAC entity may select generating aconfigured SL grant corresponding to transmission of a plurality of MACPDUs for an SL process. The MAC entity may inspect if data is availablein an STCH associated with the SL procedure. The MAC entity may performa plurality of transmission procedures for each SL process. According toOption 2, the conventional method for SL grant reception and SCItransmission may be changed as shown in Table 2.

TABLE 2   ...   1> else, if the MAC entity is configured by upper layersto transmit based on sensing using a pool of resources, the MAC entityselects to create a configured sidelink grant corresponding totransmissions of multiple MAC PDUs for a Sidelink process, and data isavailable in a STCH associated with this Sidelink process, the MACentity shall for each Sidelink process configured for multipletransmissions based on sensing:   ...

2. Resource reselection in consideration of latency requirementaccording to PPPP

Packet delay budget (PDB) may be considered as a latency requirementfrom an application layer (that is, 20 ms or 100 ms). The latency may bederived from PPPP by the AS layer, which is based on the mapping betweenthe PPPP and latency provided by configuration.

In multiple transmissions in SL mode 4, the UE allocates a time resourceand a frequency resource from a resource pool selected for periodictransmission of a V2X message (which is, for example, occurs every 500ms). Meanwhile, a time to periodically generate a V2X message may beadjusted. Due to the change of the message generation time, an allocatedperiodic resource may fail to satisfy the latency requirement (20 ms or100 ms).

For example, if a CAM generating time is adjusted by +150 ms withrespect to the same period (for example, 500 ms), the UE needs toreselect a time resource and a frequency resource from a selectedresource pool during 500 ms. Alternatively, if the CAM generating periodis changed from 500 ms to 1000 ms, the UE needs to reselect a timeresource and a frequency resource from a resource pool selectedaccording to a new period.

The UE may know a latency requirement from a PPPP associated with anSTCH. Thus, in order to appropriately satisfy a latency requirement formultiple transmissions of SL mode 4, the UE needs to be able to reselecta resource. Thus, according to an embodiment of the present invention,it may be suggested that a latency requirement derived from the PPPP isconsidered as a resource reselection trigger condition. That is, if anSL grant fails to satisfy a latency requirement from a PPPP associatedwith an MAC PDU (or associated with an STCH), reselection may betriggered. Accordingly, the conventional method for SL grant receptionand SCI transmission may be changed as shown in Table 3.

TABLE 3   ...   1> else, if the MAC entity is configured by upper layersto transmit based on sensing using a pool of resources, the MAC entityselects to create a configured sidelink grant corresponding totransmissions of multiple MAC PDUs, and data is available in STCH, theMAC entity shall for each Sidelink process configured for multipletransmissions based on sensing:   2> if SL_RESOURCE_RESELECTION_COUNTER= 0 and the MAC entity randomly selects, with equal probability, a valuein the interval [0, 1] which is above the probability configured byupper layers in probResourceKeep; or   2> if the configured sidelinkgrant cannot accommodate a RLC SDU by using the maximum allowed MCSconfigured by upper layers in maxMCS-PSSCH and the MAC entity selectsnot to segment the RLC SDU; or   2> if the configured sidelink grantcannot meet the latency requirement according to the PPPP associatedwith a MAC PDU (or associated with the STCH); or   2> if a pool ofresources is configured or reconfigured by upper layers:   3> clear theconfigured sidelink grant, if available;   3>  randomly select, withequal probability, an integer value in the interval [5, 15] and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;   3> select thenumber of HARQ retransmissions from the allowed numbers configured byupper layers in allowedRetxNumberPSSCH, and an amount of frequencyresources within the range configured by upper layers betweenminRB-NumberPSSCH and maxRB- NumberPSSCH;   3> select an integer valuein the interval [1, 10] from the allowed values configured by upperlayers in restrictResourceReservationPeriod and set the resourcereservation interval by multiplying 100 with the selected value;   3>randomly select the time and frequency resources for transmissionopportunities of SCI and SL-SCH corresponding to the number oftransmissions of MAC PDUs with the resource reservation interval fromthe resource pool, excluding the resources indicated by the physicallayer. The random function shall be such that each of the allowedselections can be chosen with equal probability;   ...

FIG. 4 shows a method for reselecting an SL resource by an MAC entity ofa UE according to an embodiment of the present invention.

In step S100, the MAC entity of the UE selects to configure a sidelinkgrant corresponding to transmission of multiple MAC PDUs. In step S110,the MAC entity of the UE determines that there is data for V2Xcommunication in an STCH. The MAC entity is configured by a higher layerto transmit based on sensing using a resource pool. The higher layer maybe the RRC layer of the UE.

In step S120, the MAC entity of the UE determines that the configuredsidelink grant cannot fulfil a latency requirement from a PPPP. In stepS130, the MAC entity of the UE reselects a sidelink resource. Thereselection of the sidelink resource may be performed for each sidelinkprocess configured for multiple transmissions based on sensing.

The reselecting the sidelink resource may include clearing theconfigured sidelink grant. Further, the reselecting the sidelinkresource may include randomly selecting, with equal probability, aninteger value in an interval between 5 and 15, and setting a value of asidelink resource reselection counter to the selected integer value.Further, the reselecting the sidelink resource may include selecting anumber of HARQ retransmissions from allowed numbers configured by theupper layer in allowedRetxNumberPSSCH, and an amount of frequencyresources within the range configured by the upper layer betweenminRB-NumberPSSCH and maxRB-NumberPSSCH. Further, the reselecting thesidelink resource may include selecting an integer value in an intervalbetween 1 and 10 from allowed values configured by the upper layer inrestrictResourceReservationPeriod, and setting a resource reservationinterval by multiplying 100 with the selected integer value. Further,the reselecting the sidelink resource may include randomly selectingtime and frequency resources for transmission opportunities of SCI andSL-SCH corresponding to a number of transmissions of MAC PDUs with theresource reservation interval from the resource pool, excludingresources indicated by a physical layer.

3. Parallel allocation for transmission of a plurality of MAC PDUs and asingle MAC PDU

Meanwhile, according to the above-described conventional method for SLgrant reception and SCI transmission, it is not clear that multipletransmissions and a single transmission are allowed to be allocated inparallel. A vehicle may transmit a periodic message and a periodicmessage (for example, DENM) triggered by an event. In this case, thevehicle is likely to allocate both the multiple transmissions and thesingle transmission. Thus, according to an embodiment of the presentinvention, it may be suggested that the UE allocates both the multipletransmissions and the single transmission in SL mode 4.

However, when an exceptional resource pool is configured through randomselection, it is obvious that the UE randomly allocate a singleopportunity. This does not mean that SL transmission in a plurality ofSL procedures is not allowed in an exceptional resource pool by randomselection. That is, according to an embodiment of the present invention,when the exceptional resource pool is configured through randomselection, it may be suggested that the UE allocates one of the multipletransmissions and the single transmission.

4. Much shorter resource reservation period for SL

In PC5-based V2V communication, traffic of a short period using a muchshorter resource reservation period may be supported. Regarding this,latency requirements for V2X communication is provided as below.

-   -   E-UTRA(N) needs to be able to transmit a message with a latency        up to 100 ms by itself or using an RSU between two UEs        supporting a V2V/P application.    -   In a specific use example (for example, sensing before a        collision), E-UTRA(N) needs to be able to transmit a message        with a latency of 20 ms at maximum between two UEs supporting a        V2X application.    -   E-UTRA(N) needs to be able to transmit a message with a latency        of 100 ms between a UE supporting a V2I application and an RSU.

Considering the above latency requirements, not just 100 ms but also 20ms should be supported as the maximum latency for SL communication.

Meanwhile, according to the above-described conventional method for SLgrant reception and SCI transmission, the UE selects an integer valuebetween [1, 10] from allowed values that are configured inrestrictResourceReservationPeriod by a higher layer, and sets a resourcereservation period by multiplying the selected value by 100. That is,100 ms, 200 ms . . . 1000 ms may be supported as the current resourcereservation period. This means that the latency requirement of 20 mscannot be satisfied as the current resource reservation period.

In some cases, a resource reservation period needs to be calculated bymultiplying a value selected between [1, 10] by 20. That is, in order toset a resource reservation period, a value by which the integer valuebetween [1, 10] is multiplied needs to be set to a variable rather thanan integer. Thus, according to an embodiment of the present invention,in order to set a resource reservation period, it may be suggested tochange the value, by which the integer value between [1, 10] ismultiplied, from 100 to a variable RSV_INTERVAL. The value ofRSV_INTERVAL may be set to 20 ms or 100 ms. Then, the UE may select aninteger value between [1, 10], and set a resource reservation period bymultiplying the selected value by RSV_INTERVAL. “10” between [1, 10] ismerely an example, and a greater integer value may be set. Accordingly,additional resource reservations such as 20 ms, 40 ms, 60 ms . . . andso on may be further supported in addition to the current resourcereservation period of 100 ms, 200 ms . . . 1000 ms.

Meanwhile, as described above, a PDB may be considered as a latencyrequirement from the application layer. The latency may be derived fromPPPP by the AS layer, which is based on the mapping between the PPPP andlatency provided by configuration. That is, a latency of 20 ms may bederived from the PPPP by the AS layer. Accordingly, each SL logicalchannel has a PPPP associated therewith, and thus, the UE may configureone or more logical channels having a latency 100 ms, or one or morelogical channels having a latency of 20 ms.

In addition, according to an embodiment of the present invention, withrespect to multiple transmissions of a plurality of MAC PDUs, it may besuggested to derive a variable RSV_INTERVAL from a PPPP related to anMAC PDU to be transmitted. In this case, multiple transmissionopportunities reserved together with resource reservation periods may beused for an STCH associated with the PPPP. Briefly, according to anembodiment of the present invention, in order for a resource reservationperiod regarding multiple transmissions of a plurality of MAC PDUs tocertainly satisfy a latency requirement derived from a PPPP associatedwith an MAC PDU or a PPPP associated with an STCH, the UE may derive thevariable RSV_INTERVAL from a PPPP associated with an STCH in which anMAC PDU to be transmitted exists

Accordingly, the conventional method for SL grant reception and SCItransmission may be changed as shown in Table 4.

TABLE 4   ...   1> else, if the MAC entity is configured by upper layersto transmit based on sensing using a pool of resources, the MAC entityselects to create a configured sidelink grant corresponding totransmissions of multiple MAC PDUs, and data is available in STCH, theMAC entity shall for each Sidelink process configured for multipletransmissions based on sensing:   2> if SL_RESOURCE_RESELECTION_COUNTER= 0 and the MAC entity randomly selects, with equal probability, a valuein the interval [0, 1] which is above the probability configured byupper layers in probResourceKeep; or   2> if the configured sidelinkgrant cannot accommodate a RLC SDU by using the maximum allowed MCSconfigured by upper layers in maxMCS-PSSCH and the MAC entity selectsnot to segment the RLC SDU; or   2> if a pool of resources is configuredor reconfigured by upper layers:   3> clear the configured sidelinkgrant, if available;   3> randomly select, with equal probability, aninteger value in the interval [5, 15] and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;   3> select thenumber of HARQ retransmissions from the allowed numbers configured byupper layers in allowedRetxNumberPSSCH, and an amount of frequencyresources within the range configured by upper layers betweenminRB-NumberPSSCH and maxRB- NumberPSSCH;   3> select an integer valuein the interval [1, 10] from the allowed values configured by upperlayers in restrictResourceReservationPeriod and the PPPP associated withthe MAC PDUs (or the PPPP associated with the STCH) and set the resourcereservation interval by multiplying the selected value with RSV INTERVALwhich is set to either 20 or 100 based on the PPPP associated with theMAC PDUs (or the PPPP associated with the STCH) (If the MAC PDUs havedifferent PPPP levels, UE selects the highest PPPP among them. UE needsto select an integer value and the RSV INTERVAL based on the delayrequirement (Packet Delay Budget) derived from the PPPP associated withthe MAC PDUs or the PPPP associated with the STCH);   3> randomly selectthe time and frequency resources for transmission opportunities of SCIand SL-SCH corresponding to the number of transmissions of MAC PDUs withthe resource reservation interval from the resource pool, excluding theresources indicated by the physical layer. The random function shall besuch that each of the allowed selections can be chosen with equalprobability;   3> if the number of HARQ retransmissions is equal to 1and there are available resources, except the resources already excludedby the physical layer for more transmission opportunities:   4> randomlyselect the time and frequency resources for the other transmissionopportunities of SCI and SL-SCH corresponding to the number ofadditional transmissions of the MAC PDUs with the resource reservationinterval from the available resources. The random function shall be suchthat each of the allowed selections can be chosen with equalprobability;   4> consider a set of transmission opportunities whichcomes first in time as the selected sidelink grant and a set oftransmission opportunities which comes later in time as theretransmission opportunities;   3> else:   4> consider the set as theselected sidelink grant;   3> use the selected sidelink grant todetermine the set of subframes in which transmissions of SCI and SL-SCHoccur;   3> consider the selected sidelink grant to be a configuredsidelink grant;   2> else if SL_RESOURCE_RESELECTION_COUNTER = 0 and theMAC entity randomly selects, with equal probability, a value in theinterval [0, 1] which is less than or equal to the probabilityconfigured by upper layers in probResourceKeep:   3> clear theconfigured sidelink grant, if available;   3> randomly select, withequal probability, an integer value in the interval [5, 15] and setSL_RESOURCE_RESELECTION_COUNTER to the selected value;   3> use thepreviously selected sidelink grant for the number of transmissions ofthe MAC PDUs with the resource reservation interval to determine the setof subframes in which transmissions of SCI and SL-SCH occur;   3>consider the selected sidelink grant to be a configured sidelink grant;  ...

FIG. 5 shows a wireless communication system to implement an embodimentof the present invention.

An eNB 800 includes a processor 810, a memory 820 and a transceiver 830.The processor 810 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 810. Thememory 820 is operatively coupled with the processor 810 and stores avariety of information to operate the processor 810. The transceiver 830is operatively coupled with the processor 810, and transmits and/orreceives a radio signal.

A UE 900 includes a processor 910, a memory 920 and a transceiver 930.The processor 910 may be configured to implement proposed functions,procedures and/or methods described in this description. Layers of theradio interface protocol may be implemented in the processor 910. Thememory 920 is operatively coupled with the processor 910 and stores avariety of information to operate the processor 910. The transceiver 930is operatively coupled with the processor 910, and transmits and/orreceives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope of the present disclosure.

What is claimed is:
 1. A method for reselecting a sidelink resource by amedia access control (MAC) entity of a user equipment (UE) in a wirelesscommunication system, the method comprising: selecting to configure asidelink grant corresponding to transmissions of multiple MAC protocoldata units (PDUs); determining that there is data for avehicle-to-everything (V2X) communication in a sidelink traffic channel(STCH); determining that the configured sidelink grant cannot fulfil alatency requirement according to a ProSe per-packet priority (PPPP); andreselecting the sidelink resource, wherein the MAC entity is configuredby an upper layer to transmit based on sensing by using a resource pool.2. The method of claim 1, wherein the reselecting the sidelink resourceis performed for each sidelink process configured for multipletransmissions based on sensing.
 3. The method of claim 1, wherein thereselecting the sidelink resource comprises: clearing the configuredsidelink grant.
 4. The method of claim 1, wherein the reselecting thesidelink resource comprises: randomly selecting, with equal probability,an integer value in an interval between 5 and 15, and setting a value ofa sidelink resource reselection counter to the selected integer value.5. The method of claim 1, wherein the reselecting the sidelink resourcecomprises: selecting a number of hybrid automatic repeat request (HARQ)retransmissions from allowed numbers configured by the upper layer inallowedRetxNumberPSSCH, and an amount of frequency resources within therange configured by the upper layer between minRB-NumberPSSCH andmaxRB-NumberPSSCH.
 6. The method of claim 1, wherein the reselecting thesidelink resource comprises: selecting an integer value in an intervalbetween 1 and 10 from allowed values configured by the upper layer inrestrictResourceReservationPeriod, and setting a resource reservationinterval by multiplying 100 with the selected integer value.
 7. Themethod of claim 6, wherein the reselecting the sidelink resourcecomprises: randomly selecting time and frequency resources fortransmission opportunities of sidelink control information (SCI) andsidelink shared channel (SL-SCH) corresponding to a number oftransmissions of MAC PDUs with the resource reservation interval fromthe resource pool, excluding resources indicated by a physical layer. 8.The method of claim 1, wherein the upper layer is a radio resourcecontrol (RRC) layer of the UE.
 9. A user equipment (UE) in a wirelesscommunication system, the UE comprising: a memory; a transceiver; and aprocessor, operably coupled to the memory and the transceiver, that:selects to configure a sidelink grant corresponding to transmissions ofmultiple media access control (MAC) protocol data units (PDUs);determines that there is data for a vehicle-to-everything (V2X)communication in a sidelink traffic channel (STCH); determines that theconfigured sidelink grant cannot fulfil a latency requirement accordingto a ProSe per-packet priority (PPPP); and reselects a sidelinkresource, wherein a MAC entity of the UE is configured by an upper layerto transmit based on sensing by using a resource pool.
 10. The UE ofclaim 9, wherein the reselecting the sidelink resource is performed foreach sidelink process configured for multiple transmissions based onsensing.
 11. The UE of claim 9, wherein the reselecting the sidelinkresource comprises: clearing the configured sidelink grant.
 12. The UEof claim 9, wherein the reselecting the sidelink resource comprises:randomly selecting, with equal probability, an integer value in aninterval between 5 and 15, and setting a value of a sidelink resourcereselection counter to the selected integer value.
 13. The UE of claim9, wherein the reselecting the sidelink resource comprises: selecting anumber of hybrid automatic repeat request (HARQ) retransmissions fromallowed numbers configured by the upper layer in allowedRetxNumberPSSCH,and an amount of frequency resources within the range configured by theupper layer between minRB-NumberPSSCH and maxRB-NumberPSSCH.
 14. The UEof claim 9, wherein the reselecting the sidelink resource comprises:selecting an integer value in an interval between 1 and 10 from allowedvalues configured by the upper layer inrestrictResourceReservationPeriod, and setting a resource reservationinterval by multiplying 100 with the selected integer value.
 15. The UEof claim 14, wherein the reselecting the sidelink resource comprises:randomly selecting time and frequency resources for transmissionopportunities of sidelink control information (SCI) and sidelink sharedchannel (SL-SCH) corresponding to a number of transmissions of MAC PDUswith the resource reservation interval from the resource pool, excludingresources indicated by a physical layer.